The invention is concerned with a process for catalyzing cationic paint binders. More particularly, the invention relates to catalyzed paint binders of the type used in cathodic electrodeposition coatings.
Cathodically depositable electrodeposition paints essentially are crosslinked at elevated temperature through transesterification, transamidation, transurethanization, or through the reaction of chain end double bonds. It is known that crosslinking reactions of this type are catalyzed with metal compounds. In practically all cases, catalyzation for the curing of cathodically depositable paint films is necessary to achieve the performance required for commercial applications. The most important catalysts used in practice are compounds of tin(IV), used mainly as dibutyltinoxide (C.sub.4 H.sub.9).sub.2 SnO or as dibutyltindilaurate (C.sub.4 H.sub.9).sub.2 Sn (OCOC.sub.12 H.sub.25).sub.2. All catalysts presently used for this purpose, however, lead to essential disadvantages in cathodically deposited electrodeposition paints.
Dibutyltinoxide is a solid substance which must be incorporated in finely distributed form in the paint and the material as a catalyst becomes effective only after dissolution. Thus, the use of this catalyst requires long periods of homogenization. When dibutyltindilaurate is employed in the paint, acid is set free through hydroylsis, which is particularly troublesome in the operation of electrodeposition installations. Furthermore, the known catalysts, in general, have poor compatibility with the resin binders of the paints. In many cases, storage stability falls off, particularly of diluted bath materials of the type which are used for replenishing electrodeposition baths.